Electrical amplifier



April 1933- P. N. BOSSART ELECTRICAL AMPLIFIER Filed Feb. 25, 1930 -+I I I I F I I I I I source such as a battery B.

Patented Apr. 25, 1933 UNi'rEnsTArss ENT O PAUL N. BOSSART, 0F SWISSV'ALE, PENNSYLVANIA, ASSIGNOR; ,TO. TI-IE UNION SWITCH &; SIGNAL COMPANY, OF SWISSVALE, PENNSYLVANIA, A CQRPORATION 0F PENNSYL- vANrA ELECTRICAL AMPLIFIER' Applicationfiled February 25, 1930.v Serial No. 431,085.

My invention relates to electrical amplifiers, and particularly to amplifiers for amplifying signals made upof modulated alternating current.

One object of my invention is to provide an amplifier of the. type described having a high degree of sensitivity and selectivityto the desired signals. a

Another object of my invention is to provide an amplifier of the type described which 'is substantially immune to shock excitation.

I will describe one form of amplifier embodying my invention, and will then point out the novel features thereof in claims.

The accompanying drawing is. a diagrammatic view illustrating one form of amplifier embodying my invention appliedto a train signaling system; i V i Signaling systems have been proposed for signaling between spaced points on a train, or between two trains, or between a train and the trackway, in which modulated alternating current is transmitted, either by unguided waves or through the medium of theitrack rails, to receiving apparatus, located in the trackway or on the train, and arranged to operate a suitable signaling device. The receiving apparatus employed in these systems may have any suitable form, but regardless of the form which the receiving apparatus takes, it is usually necessary to interpose an electrical amplifier between the receiving ap paratus and the signaling device operated thereby, in order to obtain suflicient energy to reliably actuate a signaling device of the desired ruggedness. For'this purpose, I provide the electrical amplifier illustrated in the accompanying drawing. As here shown, this amplifier comprises four electron tubes T T, T and T of the usual and well known form, each comprising a grid 5, a filament 6, and a plate 7. The filaments 6 of the tubes T T T and T are all connected in multiple and are constantly heated by current froma battery A. Plate current is supplied to each of the tubes T T T and T from a suitable Associated with the tube T is input filter, desi nat'ed in general by the reference jcharacter TD, and comprising a transformer and filament of tube T The reference character E, )referably of the air core type, having a secondary 8 divided into two parts 8 and 8?, and a primary 9 coupled with the part 8*. The primary 9 may be supplied'with the modulated signaling currentwhich itis desired to amplify in any suitable manner. For example, in those signaling systems in which the amplifier is located on the train, andthe signaling currentis transmitted through the medium of the track rails, the primary 9 may be supplied with sign aling. current by 'means of a train-carried receiver R comprising two pick-up coils l and 1, which are 'mounted on magnetizable cores2 and 29located in advance'of the forward wheels of frequency by means of a condenser 10, and are so arranged that the 'electromotive forces induced in these'coils at any instant by slignalin g currents flowing inthe' track rails are I additive.

(A condenser llis connected across the en'- tire secondary 8 of the transformer and the closed circuit'including secondary 8 and condenser 11 is tuned to resonance at the car- 'rier frequency. One terminal of condenser '11 is connected with grid 5 of tubeT by means of a wire 12, andthe other terminal of condenser llis connected with the filament 60f tube T through a grid biasing battery 0. Itwill .be apparent, therefore that when inodulatedsi-gnaling current is being supplied to the track rails 3and 3 the electromotive force which is impressed on primary '9 of transformer E by pick-up coils land 1 is stepped up bymeans of transformerv E,

afterv which it isapplied between the grid F designates a transformer, preferably having anair core, and comprising a'primary 13, and a secondary 14 constructed in two parts 14L and '14:". The primary 13 'of transformer F is included in a. plate circuit for tube T Y The secondary 14; of transformer F has a con-. denser 15 connected across its terminals which tunes the closed circuit including this condenser and secondary 14 to resonance at the carrier frequency. One terminal of condenser 15 is connected with the grid 5 of tube T by means of a wire 16, and the other terminal is connected with filament 6 of tube T through the grid biasing battery C. It will be evident therefore that the transformer F constitutes an interstage transformer by means of which the alternating component of the current in the plate circuit for tube T is made to create an alternating difference of potential between the grid and filament of tube T The parts of transformer F are preferably so proportioned that this difference of potential is greater than that impressed across the grid and filament of tube T The plate circuit for tube T includes the primary 13 of a transformer F which trans former is similar to the transformer F. .A condenser 17 is connected across the secondary 14 of transformer F and one terminal of this condenser is connected with the grid 5 of tube T by means of a wire 18 while the other terminal is connected with filament 6 of tube T through the battery C. The closed circuit including condenser 17 and secondary 14 is als'otuned to resonance at the carrier frequency.

The plate circuit for tube T includes the primary of a transformer G, This primary is made up of two parts 19 and 19 which are connected in series in such manner that any electromotive forces induced therein by stray changing fields uniform throughout the volume of the transformer G will neutralize each other. The secondary of this transformer is similarly made up of two parts 20 and 20 and this secondary is connected with the primary 25 of a high ratio step-.up transformer S through a full wave rectifier H.. The secondary 27 of trans former S is included in the grid circuit for tube T which circuit also includes the battery C. A condenser 26 is connected across the primary 25 of transformer S, and this condenser has a capacity which is large enough so that the closed circuit including primary 25 and this condenser is not tuned to resonance to any frequency near the modulation frequency. The function of this condenser will be explained more fully hereinafter. V V

' Two condensers 29 and 30 are connected between the plate and filament of tube T These condensers are the same size and have a comparatively large capacity so that any high frequency current which might flow in the plate circuit for tube T will be bypassed to the filament 6 of tube T. A reactance 31 is'connected across condenser 30, and it will be noted that due to the condenser 29 which acts as a blocking condenser, no unidirectional current flows in this reactance. A portion 31 of reactance 31 is connected with another reactance 82 through vice which it is desired to operate in accord ance with the signal received from the trackway. As here shown, this signaling device is a relay K arranged to control two electric lamps L and L in such manner that lamp L is lighted when relay K is energized, but that lamp L is lighted when relay K is deenergized. I

The tubes T T and T the input filter D, and the interstage transformers F, F and G are all shielded by suitable grounded shields indicated in the drawing by the dotted rectangles 22. The wires 12, 16 and 18 leading to the grids of tubes T T and T respectively, as well as the wires 34, 85 and 36 associated with receiver R are also shielded by suitable grounded shields indicated in the drawing by the dotted rectangles 37.

The operation of the apparatus as a whole is as follows: As pointed out hereinbefore, when the modulated alternating current employed for signaling is being supplied to the track rails 3 and 3 a corresponding modulated' alternating electromotive force is impressed across the grid 5 and filament 6v of tube T This modulated electromotive force produces variations in the plate current of tube T which, due to the interstage transformer F, causes a modulated electromotive force of similar character but of greater magnitude to be impressed across the grid 5 and filament 6 of tube T. This modulated electromotive force, in turn, causes the plate current of tube T to vary, thereby causing a similar modulated electromotive force of still greater magnitude to be impressed acrossthe grid 5 and filament 6 of tube T Variations are therefore produced in the plate current of tube T so that a modulated alternating electromotive force is induced in the secondary of transformer G. As a result, current is supplied to the primary 25 of transformer S. Due, however, to the full wave rectifier H, this current is a pulsating direct current, which rises to a maximum value at a periodicity equal to the modulationfrequency. The pulsating direct current in the primary 25 of transformer S induces an alternating electromotive force of the same frequency as the modulation frequency in the secondary 27 of transformer S, and this alternating electromotive force is impressed across the grid 5 and filament 6 of tube T. As a result, the plate current of tube T is periodically varied at the frequency of the modulations in the signaling current, and similar currents flow in reactance 31, and in the resonant circuit including condenser 33 and reactance 32. A. portion of this latter current is supplied to relay K through rectifier J, whereupon relay K becomes energized and lights lamp L as indicated in the drawing.

It is apparent from the foregoing, that when the supply of modulated carrier current to the track rails is discontinued, or,

when unmodulated carrier current is supplied to the track rails, the supply of current to relay K is interrupted. Under these conditions relay K is deenergized and lamp L is lighted.

The condenser 26 which is connected across the primary 25 of transformer S performs two functions. In the first place, it increases the strength of the desired signal by allowing a charge to collectat the peak of the maximum average value of the pulsating direct current supplied to primary 25 of transformer S, which maintains a higher electromotive force on the primary 25 of transformer S than would otherwise occur; and, in the second place, in case of shock excitation, it reduces the harmful effect for it absorbs energy and discharges it slowly through primary 25, instead of forcing a wave of steep front through transformer S as would occur if this condenser were removed.

The coupling between reactance 32 and reactance 31 is preferably small in order to increase the sharpness of the tuning of the resonant circuit including reactance 32, condenser 33, and portion 31 of reactance 31, and to adjust the output of tube T so that for a signal of normal strength, the output of this tube will be near its maximum value. I have found that with the parts proportioned in this manner, the receiver is practically immune to shock excitation from unmodulated currents having a frequency onlyslightly different from the modulation frequency.

If desired, a suitable filter, here shown as a reactor 28, may be inserted in the plate circuit of tube T to keep alternating current of modulation frequency out of battery B. Furthermore, a reactor 21 may be inserted between the battery A and the filaments of the tubes T T T and T to keep the high frequency current out of this battery.

It will be apparent therefore that I have provided an electrical amplifier possessing a high degree of sensitivity and selectivity to the modulated signaling current, but which is substantially immune to shock excitation.

While I have described an electrical amplifier embodying my invention as being particularly applicable for use in a train signaling system, it is to be understood that it is not limited to this use, but may be employed wherever an amplifier is desired for amplifying signals made up of modulated alternating current.

- -Although I have herein shown and described only one form. of'electrical amplifier embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

;Having thus described my invention, what I claim is: i v

1. An electrical'amplifier comprising an electron tube havinga grid, a plate, and a filament; a grid circuit for said tube including a sou-rce'of alternatingv current, a source of unidirectional current connected between the plate and the'filament of said first tube,

a'capacity connected between the plate and filament of said tube, a first reactance connected across a portion of saldv capacity, a second reactance,a condenser; a second on cuit including said condenser, said second re-- act-ance, and a portion of said first reacta-nce and tuned to'resonance at the frequencypf said source of alternating current g; and a signaling device responsive to current in said second circuit. 7 p y I 2. An .electrical amplifier comprising. an electron tube having agrid, a plate,. and a filament; a grid circuit for said tube including a source of alternating current, a source of unidlrectlonal current connected between the plateand the filament of said first tube, .acapacity connected between the plate and filament of said .tube, afirst reactance connected across a portionof said capacity,,a

secondreactancej, a condenser; a second ;-cir-' cuit including said condenser, said second reactance, and a portion of said first reactance and tuned to resonance at the frequency of said sourceof alternating current; a relay connected with a portion of said second re actance,and a signaling device controlled by said relay.

3. An electrical amplifier comprising a first and a second electron tube each having a grid, a filament, and a plate; a grid circuit for said first tube including a source of modulated alternating current, a first transformer having a primary and a secondary each made up of two parts connected in series I in such manner that electromotive forces induced in either said primary or said second ary by stray fields will neutralize each other,

a source of unidirectional current, a plate capacity connected between the plate and.

filament ofsaid second tube, a fourth circuit tuned to resonance atthe modulation frequency, means including a portion of said capacity for at times supplying said fourth circuit with current, and a signaling device responsive to current in said fourth circuit.

4. An electrical amplifier comprising a first and a second electron tube each having a' grid, a filament, and a plate; a grid circuit for sa1d first tube including a source of modulated alternating current, a first transformer, a source of unidirectional current, a plate circuit for said first tube including said source of unidirectional current and the primary of said first transformer, a full Wave rectifier, a step-up transformer, means for connecting the secondary of'said first transformer with the primary of said step-up transformer through said full Wave rectifier, a grid circuit for said second tube including the secondary of said step-up transformer, -means for connecting said source of un directional currentbetween theplate and filament of said second tube, a first and second condenser connected in series between the plate and filament of said secondtube, a reactance connected across said second condenser, a fourth circuit including a portion of said reactance and tuned to resonance at thc modulation frequency, a Winding, a full wave rectifier, meansincluding said rectifier for at times supplying said Winding with current from said fourth circuit, and a signal controlled by said Winding. r 1

PAUL N. BQSSART.

In testimony whereof I afiix my signature. 

